TIFR GS 2026 Question Paper with Answer Key Biology

FOR TIFR GS EXAM PREPARATION

TIFR GS 2026
Question Paper ·
Biology
EXAM YEAR TYPE SUBJECT

TIFR GS 2026 Question Paper Biology

Notes · Sample Papers · Previous Year Papers · Mock Tests

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m .co s e m TIFR GS 2026 Question Paper Biology

s e l a
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JGEEBILS (14th December, 2025) - Answer Key

1. An experiment fails 40% of times. If a student performs the experiment twice, what
is the probability she will fail the experiment once and get success once?

a. 0.16
b. 0.24
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c. 0.36
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d. 0.48
. c e m
em l as
a
2. If y is lan
sinteger a g
a
than g 5 and less
greater than 2 and less than 7 and y is also an integer greater
than 10, then we may correctly conclude that

a. y can be exactly determined
b. y may be either of two values
c. y may be any of three values
d. there is no value of y satisfying these conditions

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3. The mean of a set of 7 observations is 10 and the mean of a set of 3 observations

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is 5. The mean of the combined set is given by

e m
a. 7.5
b. 8.5 l as
c. 10
d. 15
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4. A is the father of C, and D is the son of B. E is the brother of A. If C is the sister
of D. Then B is __________________ of E.

a. Daughter
b. Husband
c. Sister – in – law
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.co
d. Brother – in law
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c. o5. A DNA molecule is 60% G + C. If one strand has 360 cytosinesbases,
e m what is the
s em total number of base pairs?
g l a
la a
ag a. 1500
b. 1200
c. 600
d. 3000

m . c
c. o s e m
s em
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TIFR GS 2026 Question Paper Biology

6. A mutation in a plant gene Z causes embryo lethality when homozygous
recessive (zz).100 plants were grown from seeds harvested from an
heterozygous parent(Zz). How many of the them will be heterozygous (Zz)?

a. 0
b. 34
c. 50
d. 66

7. Suppose you have a modern smartphone with a 48-MP camera sensor. Your
phone typically offers the option to capture images at the full 48-MP resolution or
at reduced resolutions such as 24 MP or 12 MP. How does the camera generate
these lower-resolution images from the same sensor?

a. The pixels are binned 2 or 4 times respectively to achieve the reduced
resolution

b. The reduction in resolution is achieved by cropping the field of view by 2 or 4
times respectively

c. Only every alternate or the fourth pixel respectively collects photons to achieve
the reduced resolution

d. The camera has different lenses in its rear with each lens allowing a specific
output capacity

8. Complete the following sentence. When conducting a hypothesis test, we
____________ and then evaluate the test results to determine if there is enough
evidence to ___________________.

a. Assume that the null hypothesis is false; accept the null hypothesis
b. Assume that the null hypothesis is true; reject the null hypothesis
c. Assume that the alternate hypothesis is true; reject the null hypothesis
d. Assume that the alternate hypothesis is false; reject the alternate hypothesis

9. A family has 2 children. Given that one of the children is a boy, what is the
probability that the other child is also a boy?
a. 1
b. 1/2
c. 1/3
d. 1/4

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m .co s e m TIFR GS 2026 Question Paper Biology

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10. Straight hair is a recessive trait in humans. If 64% of the population has straight
hair, what proportion of the population is heterozygous for the trait?

a. 16%
b. 32%
c. 36%
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d. 48%
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m
e on an island was infected with a virus leading to 80% mortality.glAa s
l a s
11. A bat population
a
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second
What is
wave
the
of infection immediately after lead to a 90% cumulative mortality.
percentage mortality in the second wave?

a. 20%
b. 50%
c. 85%
d. 10%

12. The price of petrol increases by 25%. By what percentage must a customer
m
reduce the consumption so that the earlier bill on the petrol does not alter?

a. 20%
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b. 25%
s e
c. 30% l a
d. 33.33% ag
13. A man walks 30 km towards the East, then, turning to the right, he walks 30 km.
Then, turning to his right, he again walks 20 km. Again, turning to his left, he
walks 30 km. How far is he from his starting point?

a. 36.05 km
b. 60.82 km
c. 30 km
m
.co
d. 58.30 km
m
c. o14. Use the table below to answer the question that follows. s em
e m la Price
las Store
ag
Discount from Manufacturer's Recommended

ag No.
1 Rs. 4 off the price of each game
2 30% discount on each game
3 One-third off the price of two games
4 buy one game and get the second at half price

m . c
c. o s e m
s em
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TIFR GS 2026 Question Paper Biology

Suman wants to buy two computer games, each of which has a manufacturer's
recommended price of Rs. 25. She checks four different stores and finds the
prices of the games discounted as shown in the table above. At which store will
Suman be able to buy the games for the least amount of money?

a. store 1
b. store 2
c. store 3
d. store 4

15. What digit does (3)31 end in?

a. 3
b. 5
c. 7
d. 9

16. The mean velocity of particles in an ideal gas is 0 and the root-mean square
velocity of the particles is ! at some temperature ". If the temperature of the gas
is increased to 2", what will be the mean and root-mean squared velocity of the
gas respectively?

a. 0, !
b. 0, 2!
c. 0, √2!
d. !, 2!

17. The average time for a molecule to diffuse from the centre of a cell of radius ' to
its boundary is (. If the cell radius is doubled, but the diffusion constant of the
molecule doesn't change, the average time now becomes:

a. 2(
b. 4(
c. 0.5(
d. 0.25(

18. Assume a spherical cell takes in nutrients at a rate proportional to its surface
area, but to divide needs a total amount proportional to its volume. Let ( be the
time a cell of radius ' takes to accumulate the nutrients it needs to divide. If ' is
doubled, what happens to (?

a. Doubles
b. Is halved
c. Stays the same

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m .co s e m TIFR GS 2026 Question Paper Biology

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d. Quadruples

19. A plant cell placed in a sucrose solution exhibits an osmotic pressure of 0.2 MPa
when the sucrose concentration is 0.1 mol/L and temperature is 300 K. If the
concentration is doubled, what will be the new osmotic pressure (assuming ideal
behavior)?
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a. 0.1 MPa
. c e m
b. 0.2 MPa
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l as
c. 0.4 MPa
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d. 0.8 MPa
a
20. An enzyme-catalyzed reaction is operating at a substrate concentration that
makes the reaction rate very close to the maximum ,!"# . If the substrate
concentration is halved but remains well above the Michaelis constant -! , what
happens to the reaction rate?

a. Halves
b. Remains near ,!"#
c. Doubles
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d. Drops close to zero
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21. There is a latent heat associatedlawith converting water at 273K to ice at 273K.
This latent heat is needed ag

a. to cool down the water molecules
b. to change the entropy of the molecules
c. to heat up the water molecules
d. there is no latent heat associated with freezing.

22. What is the maximum volume . of a sphere that can be carved out of a cube of
m
.co
side /?
m
m .co $" !
s e m
la
a.
s e %
g
g la a
a
&$" !
b.
'

$" "
c.
&

$" !
d.
'

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c. o s e m
s em
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TIFR GS 2026 Question Paper Biology

" (
23. Let the equation of for energy be 0(2) = #" − $ where 2 has the dimension of
# #
the distance. What is the unit of b?

a. kg m⁸ s⁻²
b. kg m⁶ s⁻²
c. kg m¹⁰ s⁻²
d. kg m⁴ s⁻²

24. You are standing at the center of a circle of radius '. And an object of mass m is
moving along the circumference of the circle with velocity !. What is the angular
momentum of the object that you would measure?

a. 7!'
b. 7!/'
c. 7') !
d. 7! ) '

25. You have been given two blocks of copper:- Block-A having Weight = 2 kg and
Block-B having weight = 5 kg. Both the blocks are kept at the same temperature. The
specific heat of Block-A is ________

a. the same as the specific heat of Block-B
*
b. times the specific heat of Block-B
)
)
c. times the specific heat of Block-B
*
d. 5 times the specific heat of Block-B

26. Two objects P and Q are launched at the same time and place from ground on
the Moon (no friction from air). Object P is launched with speed 25 m/s at an
angle of 9 from the horizon. Object Q is launched with speed 25 m/s at an angle
of 9 + 60°. What is the distance between P and Q after two seconds. At this
moment neither P nor Q has hit the ground yet.

a. 25√5 m
b. 30 m
c. 50 m
d. 125 m

27. In the RC circuit below, an AC voltage input of 50 Hz frequency results in a peak
current of :+ through the capacitor. If the frequency of the input voltage is
increased to 100 Hz keeping its amplitude unchanged, the peak current through
the capacitor becomes :+ ′. Which of the following is correct?

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m .co s e m TIFR GS 2026 Question Paper Biology

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a. :+ ′ = 0.5 :+ m
om
b. :+, = 0.25 :+
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c. :+ ′ = :+
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d. :+ ′ = 2 :+
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l your data on a log-log graph (log to the base 10) which is well described
byaagstraight line with slope 1/2 and intercept -1. What is the nature of the
28. You plot

function that you are plotting?
-
a. < = √2
-.

-
b. < = 2−1
-.

c. < = 10x )
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d. < = 10√x
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l a
gof these numbers is closest to the probability that
29. You roll a dice 4 times. Which a
you will roll a 6 at least once.

a. 0.004
b. 0.66
c. 0.16
d. 0.52

30. Find the angle between two vectors ?⃗ and A B⃗ , if the magnitude of their cross
m
m product is the same as that of their dot product.
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m .co s e m
s e a. 0o
g la
g la b. 180o
a
a c. 90o
d. 45o

31. fluorescent chemical probe is designed to selectively react with cysteine residues
in proteins. Which of the following would be most appropriate for selective
cysteine labeling?

m . c
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s em
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TIFR GS 2026 Question Paper Biology

a. NHS ester
b. Maleimide
c. Azide
d. Alkyne

32. A mutation that replaces a serine residue with alanine in a protein is likely to:

a. Increase the surface area of the protein
b. Introduce a new hydrogen bond donor
c. Prevent phosphorylation at that site
d. Increase the protein’s hydrophilicity

33. You want to label glycoproteins on the surface of live mammalian cells using click
chemistry. You feed the cells an azide-modified sugar that gets incorporated into
cell-surface glycans, then add a fluorescent alkyne probe. Which observation
would most strongly suggest successful, specific labeling?

a. Fluorescence signal is localized to the plasma membrane and is lost when
azide sugar is omitted
b. Fluorescence signal appears uniformly throughout the cytoplasm
c. Fluorescence is only seen after fixing the cells with paraformaldehyde
d. Fluorescence appears in mitochondria

34. In the Jablonski diagram shown below, solid arrows are radiative processes and
a dashed arrow is a non-radiative process. Which option describes this figure
correctly for an organic fluorophore?

a. X is fluorescence, Y is phosphorescence, Z is internal conversion, and Z is
the fastest
b. X is fluorescence, Y is internal conversion, Z is phosphorescence, and Z is
the slowest

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m .co s e m TIFR GS 2026 Question Paper Biology

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c. X is fluorescence, Y is intersystem crossing, Z is phosphorescence, and Z
is the fastest
d. X is fluorescence, Y is intersystem crossing, Z is phosphorescence, and X
is the fastest

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35. One litre of a solution of pH 2 is mixed with two litre of another solution of pH 3.
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c
Which of the following values describes the pH of the mixture accurately? Hint:
. e m
log102=0.3
e m l as
a s
a.l 2.3 ag
g
a b. 2.4
c. 2.5
d. 2.6

36. Under certain conditions CO2 melts rather than sublimes (transition from solid to
gas). To which transition in the phase diagram does this change correspond?

m
m .co
s e
l a
ag

a. A àB
m
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b. BàC
m
.co
c. CàA
d. AàC e m
e m las
las ag
ag 37. Consider the following two reactions.

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c. o s e m
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TIFR GS 2026 Question Paper Biology

Which one of the following combinations of coenzymes is correct?

a. P and S = NAD+ ; Q and R = NADH + H+
b. P and R = NADH + H+ ; Q and S = NAD+
c. P and R = NAD+ ; Q and S = NADH + H+
d. P and S = NADH + H+ ; Q and R = NAD+

38. Given below are experimental measurements of thermodynamic parameters for
interaction between a protein and 4 different ligands. Which one of the following
ligands has the highest affinity for the protein, based on estimates of dissociation
constant derived from the data below?

Ligand DG (kcal/mol) DH (kcal/mol) DS (kcal/mol/K)
Lig1 - 8.5 - 2.5 + 0.02
Lig2 - 3.5 + 2.5 + 0.02
Lig3 - 4.5 - 1.5 + 0.01
Lig4 + 4.5 - 1.5 - 0.02

a. Lig1
b. Lig2
c. Lig3
d. Lig4

39. Given below is the graph representing the unfolding of a protein.

Which one of the following options corresponds to the enthalpy change (in kcal/mol)
accompanying unfolding of the protein, given that the entropy change is 2.5
kcal/mol/K?

a. 0.008

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m .co s e m TIFR GS 2026 Question Paper Biology

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b. - 0.0625
c. - 100
d. 782.5

40. A mixture of the following amino acids is subjected to paper electrophoresis at
pH = 3.9: Ala, Phe, Ser, Arg, His and Asp. The PI for Ala, Phe and Ser are near
pH = 6, while that for Arg, His and Asp are 10.8, 7.6 and 3 respectively.
o m
i. Ser, Phe and o m . c
. cmove
Ala will move towards cathode and would not separate.
e m
emArg will move towards cathode and will separate out from the above
ii. Asp will also towards the cathode.
l as
l s
iii. His and
a acids. ag
g
3 amino
iv.aHis and Ser will move towards the anode.

Based on this information, choose the statements from the below that are correct:

a. (i), (ii) and (iii)
b. (i) and (iii)
c. (ii) and (iii)
d. (iii) and (iv)

o m
c
41. Calculate the mass of the analyte from .the following mass spectra.
e m
l as
ag

m
m .co
m .co s e m
s e g la
g la a
a
a. 1000
b. 1001
c. 250
d. 500

m . c
c. o s e m
s em
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TIFR GS 2026 Question Paper Biology

42. Which of the following is aromatic?

a. i
b. ii
c. iii
d. iv

43. Two dyes differ primarily in the presence of a xanthene core with different
substituents, which affects their absorption and emission maxima. Dye (1)
absorbance maxima is ~488 nm. The absorbance of dye (2) is red shifted to ~ 549
nm. Based on this information and the structures shown here, what would be the
absorbance maxima of dye (3)?

a. More than 549 nm
b. Less than 488 nm
c. More than 488 nm but less than 549 nm
d. 549 nm

44. The rate constant of a second-order reaction ? + A → E follows FGH-. I = 30 −
%...
, where the temperature " = 270 E . The value of the rate constant, I is
/

a. 10-192

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m .co s e m TIFR GS 2026 Question Paper Biology

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b. 102
c. 1010
d. 7.78

45. Which of the following graphs correctly represents the equilibrium condition?
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. c e m
em l as
l as ag
ag

m
m .co
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a. A
b. B
c. C
d. D

46. To increase the stability of RNA, replace the 2' OH with

m
m a. Amine (NH2)
.co
.co m
b. Thiol (SH)
m c. Methoxy (OCH3)
s e
s e d. Selenol (SeH)
g la
g la a
a 47. A bacterial operon is negatively regulated by a repressor that is inactivated by
lactose. Which of the following changes will result in constitutive expression?

a. Mutation in the promoter sequence
b. Mutation in the repressor binding site of the operator

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c. o s e m
s em
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TIFR GS 2026 Question Paper Biology

c. Mutation in the gene encoding beta-galactosidase
d. Mutation that increases repressor affinity for operator

48. Two yeast mutants (A and B) both fail to synthesize leucine. When mated, the
diploid regains the ability to grow without leucine. Which inference is correct?

a. Mutations A and B are in the same gene
b. Mutations A and B are in different genes of the same pathway
c. The cross reverts one mutation
d. Both mutations affect a non-genetic process

49. You study a signaling pathway with three proteins: A, B and C. These are
required for transcriptional activation of a gene X.
Mutant A⁻ has no activation; mutant B⁻ also has no activation; mutant C⁻ has
strong basal activation. When you overexpress C in A⁻ background, activation is
restored. What is the best possible inference given the above data?

a. C acts upstream of A
b. C acts downstream of A
c. A negatively regulates C
d. B activates C

50. You test two yeast mutants affecting mitochondrial morphology.

Genotype Mitochondrial morphology

WT Tubular

Δfzo1 Fragmented

Δdnm1 Hyperfused

Δfzo1 Normal
Δdnm1

Q: Which is the best possible explanation?

a. fzo1 and dnm1 act in the same pathway.
b. fzo1 promotes fission, dnm1 promotes fusion.

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m .co s e m TIFR GS 2026 Question Paper Biology

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c. dnm1 acts downstream of fzo1.
d. fzo1 and dnm1 balances the system.

51. A mutation eliminates the signal peptide of a secretory protein. Where would the
mature protein localize?

a. Accumulate in the ER lumen m
om
b. Be degraded in lysosomes
. co
. c
c. Remain in cytosol
e m
m
d. Be secreted normally
e l as
as ag
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52. Aabiochemical pathway involves sequential enzymes E₁, E₂, and E₃.
A mutation in E₂ leads to accumulation of compound X and deficiency of final
product Y. Which experimental result would confirm feedback inhibition by Y on
E₁?

a. Addition of Y decreases the level of X
b. Addition of Y increases the level of X
c. Addition of Y has no effect on X
d. Addition of X decreases the synthesis of Y
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m .co
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53. The Mars Rover returns to earth after 20 years and brings back soil samples from
l a
ag
Mars. Examination of the soil samples results in the identification of fossils from
which a compound resembling protein is isolated. You obtain a sample of Martian
protein and analyze its composition. After much hard work you were able to identify
68 amino acids in this protein sample. Assuming that Martian DNA has four bases
what is the minimum number of bases that need to be present in a codon to
represent all 68 amino acids in the genome?

a. A triplet code
b. A doublet code
c. A quadruplet code
m
.co
d. A quintuplet code
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m .co s e m
s e g la
g la a
a

m . c
c. o s e m
s em
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TIFR GS 2026 Question Paper Biology

54. In the schematic that defines the flow of information in the Central Dogma of
molecular Biology, which pathways (numbers) for the flow of information have not
been discovered?
1

4 6
7 8

9

5

2 3

a. 6
b. 4
c. 7
d. 2

55. In sea urchin DNA, which is double-stranded, 17% of the bases were shown to
be cytosine. The percentages of the other three bases expected to be present in
this DNA are:

a. G = 8.5%, A = 50%, T = 24.5%
b. G = 34%, A = 24.5%, T = 24.5%
c. G = 17%, A = 17%, T = 17%
d. G = 17%, A = 33%, T = 33%

56. You design a GFP reporter driven by a promoter of gene Y, which is repressed
by protein Z. You knock out Z gene and GFP levels shoot up but gradually return
to baseline after 24 hrs. RT-qPCR shows Y mRNA also decreases back to
baseline.
Q: What could explain this transient activation?

a. Z is redundant with another repressor.
b. Y indirectly activates a feedback that re-expresses Z.
c. GFP destabilizes Y promoter.
d. Knockout of Z caused increased translation.

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m .co s e m TIFR GS 2026 Question Paper Biology

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a ag
57. Mantis shrimps express dozens of opsins genes. Each opsin has a slightly different
peak sensitivity to different wavelengths of light and hence confers a different color
sensitivity to the shrimp. A researcher sequenced the opsin genes of 5 different
species in the Indian and Pacific Ocean and mapped their opsin expression onto
their phylogenetic relationships. See the following to answer the question below:
m
om . co
. c e m
em l as
l as ag
ag

m
m .co
s e
a
Q: Based on the phylogenetic relationship shown above, the opsin gene with red
l
ag
sensitivity evolved at which node?

a. Node marked with a star
b. Node marked with a rectangle
c. Node marked with the circle
d. Node marked with a triangle

58. Male frogs attract females with their mating calls. These calls include both visual
and acoustic signals: females prefer males with louder calls (auditory) and large
inflating vocal sacs (visual). To understand the relative contribution of the two
m
m sensory signals, researchers placed 4 dummy frogs at equal distances and
.co
m .co released a female frog in the middle. Dummy frog A did not make any sound or
s e m
la
vocal sac movements, dummy frog B made only sound calls, dummy frog C made
s e only vocal sac movements, but no sound and dummy frog D produced both sounds
g
g la and vocal sac movement. The researchers quantified the number of approaches a
a towards each dummy frog as an indicator of female preference. Based on the data
below, which of the following is true?

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c. o s e m
s em
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TIFR GS 2026 Question Paper Biology

a. (A)Female frogs have a stronger preference for visual signal (vocal sac
inflation) as compared to the auditory signal

b. (B)Female frogs have a stronger preference for auditory signal as compared
to the visual signal

c. (C)Female frogs show strongest preference for males that display both
visual and auditory signals together

d. Both b and c

59. Hepatocytes harbor the cellular organelles called peroxisomes, while both
hepatocytes and peroxisomes can be assumed as spherical. If hepatocytes have
diameter in the range of 20-30 μm, and peroxisomes in the range of 0.1-1 μm,
what is the closest estimated number of peroxisomes inside a hepatocyte with
20% of the peroxisomal volume, considering average diameters for both?

a. ~3000
b. ~25 X 103
c. ~11 X 108
d. ~500

60. You are being given a restriction map of a plasmid. How many fragments will you
get If you cut the plasmid with the restriction enzyme EcoRI and BamHI?

BamHI sites: 5, 5325, 7838
EcoRI sites: 455, 2968, 8835

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m .co s e m TIFR GS 2026 Question Paper Biology

s e l a
a ag
a. 4
b. 5
c. 6
d. 3

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l as ag
ag

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s e
l a
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m
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m .co s e m
s e g la
g la a
a

m . c
c. o s e m
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